Driving circuit for use with high voltage bidirectional semiconductor switches

ABSTRACT

A driving circuit for a half bridge utilizing bidirectional semiconductor switches in accordance with an embodiment of the present application includes a high side driver operable to control a high side bidirectional semiconductor switch, wherein the high side driver provides a negative bias voltage to the bidirectional semiconductor switch to turn the high side bidirectional semiconductor switch OFF. A low side driver may be operable to control a low side bidirectional semiconductor switch. An external voltage source with a negative terminal of the voltage source connected to the high side driver may be provided. A high side driving switch may be positioned between the negative terminal of the voltage source and the high side driver and operable to connect the high side driver to the negative terminal of the voltage source when the low side driver turns the low side bidirectional semiconductor switch ON.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims benefit to and priority from U.S.Provisional Patent Application No. 60/670,829 entitled DRIVING CIRCUITSAND TECHNIQUES FOR HIGH VOLTAGE, BIDIRECTIONAL SEMICONDUCTOR SWITCHESfiled Apr. 13, 2005, the entire contents of which are herebyincorporated by reference herein.

The present application also claims benefit and priority from U.S.Provisional Patent Application No. 60/680,629 entitled DRIVING CIRCUITAND TECHNIQUE FOR HIGH VOLTAGE BIDIRECTIONAL SEMICONDUCTOR SWITCHESfiled May 13, 2005, the entire contents of which are hereby incorporatedby reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to driving circuits and methods for usewith high voltage bidirectional semiconductor switches. In particular,the present invention provides for a driving circuit that utilizes abootstrap capacitor and a driving circuit with self supply from a DCbus.

2. Related Art

Recently developed bidirectional III-nitride switches are particularlyuseful in the field of high power and high frequency electronics. Abidirectional III-nitride switch typically includes a substrate whichmay be composed of Si, SiC, Sapphire, or the like, a first semiconductorbody formed over the substrate comprised of gallium Nitride (GaN), and asecond semiconductor body formed over first semiconductor body andcomposed of AlGaN. The heterojunction of GaN and AlGaN produces a highlyconductive two-dimensional electron gas (2DEG) at or near theheterojunction. The 2DEG is formed due to the spontaneous polarizationeffect as is known in the art. Two Ohmic power electrodes are ohmicallyconnected to the second semiconductor body (AlGaN). Two gate electrodesmay be positioned a predetermined distance from each of the two ohmicresistors. The bidirectional III-nitride switch described above is adepletion mode device in that it is normally ON. The application of anappropriate voltage to either of the gates, however, causes aninterruption of the 2DEG which turns the switch OFF. Generally, thevoltage that is applied to the gate or gates to turn the switch OFF is avoltage that is more negative than the potential at either of the ohmicelectrodes. Additional and non-limiting examples of bidirectionalswitches can be found in U.S. Patent Publication No. 2005/0189561entitled III-NITRIDE BIDIRECTIONAL SWITCH, filed on Feb. 11, 2005 in thenames of Daniel M. Kinzer and Robert Beach and assigned to the assignedof the present application, the contents of which are herebyincorporated by reference.

The bidirectional switches discussed above are particularly useful foruse in high voltage, high frequency systems and as such are useful formost any power electronics application over a wide range of topologies.

However, given the somewhat unique characteristics of these switches asdepletion mode devices, it is desirable to provide improved drivingcircuits and methods to control these switches.

SUMMARY OF THE INVENTION

A driving circuit for a half bridge utilizing bidirectionalsemiconductor switches in accordance with an embodiment of the presentapplication includes a high side driver operable to control a high sidebidirectional semiconductor switch, wherein the high side driverprovides a negative bias voltage to the bidirectional semiconductorswitch to turn the high side bidirectional semiconductor switch OFF, alow side driver operable to control a low side bidirectionalsemiconductor switch, an external voltage source wherein the a negativeterminal of the voltage source is connected to the high side driver; anda high side driving switch, positioned between the negative terminal ofthe voltage source and the high side driver and operable to connect thehigh side driver to the negative terminal of the voltage source when thelow side driver turns the low side bidirectional semiconductor switchON.

A driving circuit for a half bridge utilizing bidirectionalsemiconductor switches in accordance with another embodiment of thepresent application includes a high side driver operable to control ahigh side bidirectional semiconductor switch, wherein the high sidedriver includes a linear regulator control device that selectivelyconnects the high side driver to a lower rail of the half bridge and alow side driver operable to control a low side bidirectionalsemiconductor switch.

Other features and advantages of the present invention will becomeapparent from the following description of the invention which refers tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a driving circuit for use with a half bridge circuitutilizing bidirectional switching devices in accordance with anembodiment of the present application.

FIG. 2 is a schematic illustration of a simulation circuit used tosimulate the circuit of FIG. 1.

FIG. 3 is a chart illustrating measured gate-source voltages of theswitching devices illustrated in the simulation circuit of FIG. 2.

FIG. 4. Is a chart illustrating measure gate-source voltages of theswitching devices and illustrating the dead time during which bothswitched are off of the circuit of FIG. 2.

FIG. 5 is a chart illustrating the gate-source voltage of the switchesof FIG. 2 and the load voltage and current.

FIG. 6 illustrates a driving circuit for use with a half bridge circuitutilizing bidirectional switching devices in accordance with anembodiment of the present application.

FIG. 7 illustrates a schematic of a simulation circuit used to simulatethe circuit of FIG. 6.

FIGS. 8A-8C are charts illustrating simulated values of variousparameters in the circuit of FIG. 7.

FIG. 9 is a chart illustrating measured values of the gate-sourcevoltages of the switching devices in the simulation circuit of FIG. 7.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

One of the advantages of using double gated bidirectional semiconductorswitches such as those described above, with regard to the topology ofaccompanying driving circuits is the possibility of having fullyequivalent gates each referred to a device source. For example in thespecific circuit illustrated in FIG. 1, a gate of a bidirectionalsemiconductor switching device (108 or 110) is referenced to thepositive DC bus rail (VBUS), the negative DC bus rail (RTN) and the halfbridge output (node 103).

Further, given the fact that bidirectional semiconductor switches aredepletion mode devices which are normally ON and typically require anegative bias on at least one gate in order to be turned OFF, newdriving topologies are possible.

The circuit of FIG. 1 illustrates a first topology of a driving circuitfor a half bridge utilizing bidirectional semiconductor switches 108,110 in accordance with an embodiment of the present invention.

As illustrated in FIG. 1, two bidirectional semiconductor devices,specifically a high side switch 108 and a low side switch 110 arearranged in series between the positive DC bus rail (VBUS) and negative,or lower, DC bus rail, or return rail (RTN). A node 103 is providedbetween the high side and low side switches 108, 110 at the output ofthe half bridge which is preferably coupled to a load (not shown).

A driving circuit 100 is provided to control the switches 108 and 110 ofthe half bridge. In the particular embodiment illustrated in FIG. 1, thedriving circuit is implemented as an integrated circuit (IC) formed on a20V bulk substrate 102 with 2 floating wells 104, 106. The first well(HV1) 104 preferably has a 600V capacity and includes components fordriving the high side switch 108. The second well (HV2) 106 preferablyhas a 20V capacity.

The high side bidirectional switch 108 is preferably driven by aconventional output buffer formed by transistors Q1 and Q2 positioned inthe first floating well 104. As illustrated, a node 116 is positionedbetween transistors Q1 and Q2 and is coupled to one of the gates ofswitch 108. The ON/OFF status of the transistors Q1 and Q2 is preferablydetermined based upon a high side input logic control signal HI which isconnected to the circuit 100 via the bulk. It is noted that the ICcircuit may also include appropriate level shifting and delay functionscommon to conventional driving circuits to ensure that the high sideinput logic control signal HI provide proper control.

In operation, the high side switch 108 is nominally ON and thus conductsto provide a voltage to the load via the output node 103 of the halfbridge. During this time, the transistor Q2 is preferably OFF, andtransistor Q1 is preferably ON. Thus no voltage is provided to the gateof the switch 108. The switch 108 remains ON since no voltage is appliedto the gate connected to node 116 and the voltage at the other gate ofthe switch 108 is the same as that of the positive DC bus rail and thusno negative bias voltage applied either gate. When desired, the switch108 may be turned OFF based on the high side logic signal HI. Inparticular, the switch Q2 is turned ON, and switch Q1 is turned off,such that a negative voltage is provide to the node 116 via thetransistor Q2 and the high voltage MOSFET 114 (Mbs) from the negativeterminal of voltage source 109. This negative voltage can then beapplied to the lower gate of the switch 108, thus providing the negativebias to turn this switch OFF.

Just as in a conventional drive circuit for use with a conventional halfbridge, the high side switch 108 and the low side switch 110 should notbe ON at the same time. Thus, when the high side switch 108 is ON, thelow side switch 110 should be OFF. Similarly, when the low side switch110 is ON, the high side switch 108 is OFF. The high side logic input HIand low side logic input LI thus are provided to ensure that theswitched 108 and 110 are never ON at the same time.

Thus, when the high side logic input HI drives the switch 108 OFF, thelow side logic input LI preferably is used to turn the low side switch110 ON. It is noted however, that the IC 100 may also be provided withan appropriate dead time (DT) to ensure that the high side and low sideswitches 108 and 110 are not ON at the same time during the transition.The use of such a preset dead time is common in driving circuits. Thelow side switch 110 is preferably controlled by cascoded switching. Thatis, power MOSFET 112 is placed in series between the switch 110 and thelower rail of the DC bus. The top gate of the switch 110 is coupled tothe top electrode thereof, and thus will not provide a negative biasrelative to the top electrode. The bottom gate of the switch 110 iscoupled to the lower DC BUS rail, or return rail RTN. Thus, thepotential applied to the lower gate will be substantially constant.However, the low side input logic LI is preferably used to control theoutput buffer formed by transistors Q3 and Q4 in the second well 106.Again, appropriate level shifting and delays may be incorporated intothe IC 100 to ensure that the low side input logic LI providesappropriate control. A node 118 is provided between the transistors Q3and Q4 to provide a voltage to turn the power MOSFET 11 ON and OFF. Whenthe power MOSFET is ON, the relationship of the potential applied to thegates of switch 110 is such that the switch 110 stays on. When the powerMOSFET 110 is turned OFF however, the voltage at the low side electrodeof the switch 110 will change such that the switch 110 is turned OFF.

As illustrated, the node 118 also controls the high voltage MOSFET 114as well, such that the High voltage MOSFET is only ON when the powerMOSFET 112 is ON. In particular, it is preferable if there is a slightdelay between the turning ON of the power MOSFET 112 and the turning ONof the high voltage MOSFET such that the high voltage MOSFET 114 turnson only after the power MOSFET 112 is already ON. Similarly, it ispreferable that the high voltage MOSFET 114 turn OFF before the powerMOSFET 112 turns OFF.

In addition, a desaturation control device 120 is provided to ensurethat the power MOSFET 112 remains unsaturated. This feature is desirablein order to ensure that control of the power MOSFET will result incontrol of the lower switch 110.

The only external components used by the IC 100 are the two capacitorsC1 and C2 and the single Diode D2. It is noted that the Diode D2 mayalso be incorporated into the IC if desired. This may be preferable inorder to more easily provide short circuit protection, current sensingor temperature sensing.

In addition, it is noted also that using the configuration illustratedin FIG. 1, the capacitor C1 can be charged via the low side switch 110,the power MOSFET 112 and the high voltage MOSFET 116 when the high sideswitch 108 is turned OFF.

FIG. 2 is an illustration of a circuit used to simulate the circuitillustrated in FIG. 1. The circuit of FIG. 2 utilizes a half bridgedriver chip such as the IR2109(4) manufactured by InternationalRectifier Corporation to substantially provide the components of theintegrated circuit 100 described above. The function and layout of theIR2109(4) is well known and publicly documented and thus will not bedescribed in detail herein. It will be understood, however, that otherfunctionally equivalent driver chips may also be used.

As illustrated in FIG. 2 the external capacitors C1 and C2 are connectedbetween appropriate pins of the chip. The transistor M1 illustrated inFIG. 2 and labeled HV MOSFET corresponds to the high voltage MOSFET 114of FIG. 1. Bidirectional semiconductor switches HEMT2 and HEMT1correspond to the bidirectional switches 108 and 110 of FIG. 2. Theadditional components illustrated in FIG. 2 include modifications andadaptations necessary for testing.

FIG. 3 is a chart illustrating measured values of the gate-sourcevoltages (VGS) for the high side and low side switches HEMT2, HEMT1 inFIG. 2. As illustrated the gate-source voltages for both switchedtransition between positive and negative values such that they would becapable of turning the bidirectional switches ON and OFF as necessary.

FIG. 4 is another chart illustrating measured values of the gate-sourcevoltages (VGS) for the high side and low side switches HEMT2, HEMT1 inFIG. 2. FIG. 4 further highlights the dead time provide between changesin gate-source voltage in switches of FIG. 2 during which both switchedare OFF. In addition the SWN is also illustrated.

FIG. 5 is a chart illustrates the measured values for the load current(Iload), the load voltage (Vload) and the gate source voltage of the lowside switch (HEMT1) of FIG. 2) along with the measure SWN.

FIG. 6 illustrates a second topology of a driving circuit for a halfbridge utilizing bidirectional semiconductor switches in accordance withanother embodiment of the present invention.

The circuit of FIG. 6 includes many common elements as that of FIG. 1and thus common element will be referred to with common referencenumerals.

As in FIG. 1, FIG. 6 illustrates two bidirectional semiconductordevices, specifically a high side switch 108 and a low side switch 110are arranged in series between the positive DC bus rail (VBUS) andnegative, or lower, DC bus rail, or return rail (RTN). The node 103 isprovided between the high side and low side switches 108, 110 at theoutput of the half bridge which is preferably coupled to a load (notshown).

A driving circuit 600 is provide to control the switches 108 and 110 ofthe half bridge. In the particular embodiment illustrated in FIG. 6, thedriving circuit is implemented as an integrated circuit (IC) formed on a20V bulk substrate 102 and a single floating well (HV1) 602 whichpreferably has a 600V capacity and includes components for driving thehigh side switch 108.

The high side bidirectional switch 108 is preferably driven by aconventional output buffer formed by transistors Q1 and Q2 positioned inthe first floating well 602. As illustrated, the node 116 is positionedbetween transistors Q1 and Q2 and is coupled to one of the gates ofswitch 108. The ON/OFF status of the transistors Q1 and Q2 is preferablydetermined based upon a high side input logic control signal HI which isconnected to the circuit 100 via the bulk. It is noted that the ICcircuit may also include appropriate level shifting and delay functionscommon to conventional driving circuits to ensure that the high sideinput logic control signal HI provide proper control.

In operation, the high side switch 108 is nominally ON and thus conductsto provide a voltage to the load via the output node 103 of the halfbridge. During this time, the transistor Q2 is preferably OFF, andtransistor Q1 is preferably ON. Thus no voltage is provided to the gateof the switch 108. The switch 108 remains ON since no voltage is appliedto the gate connected to node 116 and the voltage at the other gate ofthe switch 108 is the same as that of the positive DC bus rail and thusno negative bias voltage applied either gate.

The linear regulator control device 604 is also preferably provided inthe well 602 and monitors the voltage across the capacitor C23 and thestatus of the switch 108. The linear regulator control device 604controls high voltage transistor 606 (Mlin) to power the output bufferformed by the transistors Q1 and Q2. As noted in FIG. 6, the highvoltage transistor 606 (Mlin)is preferably a p-channel device. If thevoltage across the capacitor C23 falls below a threshold level, forexample, 12 volts in the specific circuit illustrated in FIG. 6, thetransistor 606 is switched ON to ensure that there is a path to chargethe capacitor C23 whether or not the switch 108 is ON. If the switch 108is ON the transistor 606 is turned ON if the voltage across capacitorC23 is above the threshold voltage. If the voltage across capacitor C23is above the threshold level, it may be an indication that the loadvoltage at node 103 is rising too high in which case it is preferable toturn switch 108 OFF. In conjunction with the high side input logic HIthe low voltage of the return rail (RTN) is provided to the node 116 isprovide via the transistor 606 and the transistor Q2, which ispreferably turned ON bu the logic signal HI. The voltage at node 116will be negative with respect to the high side rail and the outputvoltage, and thus will shut switch 108 OFF. As noted above whentransistor Q1 is ON and transistor Q2 is OFF, no voltage is applied tothe gate of switch 108 and the switch remains ON. Low voltage diode D3may be provided in the linear regulator loop to help prevent thecapacitor C23 from discharging when the high side switch 108 is OFF andlow side switches 110 and 112 are ON.

As noted above with respect to FIG. 1 the low side logic input LIpreferably is used to turn the low side switch 110 ON and OFF asdesired. The power MOSFET 112 may be placed in series between the switch110 and the lower rail of the DC bus. The top gate of the switch 110 iscoupled to the top electrode thereof, and thus will not provide anegative bias relative to the top electrode. The bottom gate of theswitch 110 is coupled to the lower DC BUS rail, or return rail RTN.Thus, the potential applied to the lower gate will be substantiallyconstant. However, the low side input logic LI is preferably used tocontrol the output buffer formed by transistors Q3 and Q4. Appropriatelevel shifting and delays may be incorporated into the IC 600 to ensurethat the low side input logic LI provides appropriate control. A node118 is provided between the transistors Q3 and Q4 to provide a voltageto turn the power MOSFET 112 ON and OFF. When the power MOSFET is ON,the relationship of the potential applied to the gates of switch 110 issuch that the switch 110 stays on. When the power MOSFET 110 is turnedOFF however, the voltage at the low side electrode of the switch 110will change such that the switch 110 is turned OFF.

The desaturation control device 120 may also be provided to ensure thatthe power MOSFET 112 remains unsaturated. This feature is desirable inorder to ensure that control of the power MOSFET will result in controlof the lower switch 110.

The integrated circuit 600 of FIG. 6 eliminates the need for theexternal power supply 109 from FIG. 1 and also ensures safe start up andefficient voltage regulation by avoiding transient effects on the linearcircuitry.

FIG. 7 is a schematic of a simulation circuit used in testing thecircuit of FIG. 6. FIGS. 8A-8C are charts illustrating measured valuesof various parameters of the circuit of FIG. 7. As illustrated in FIG.8A for example which is a graph of the output voltage V4, from start upthe output voltage V4 rises smoothly to the desired value and thenremains at the desired value.

FIG. 9 is a chart illustrating the measured values of the gate-sourcevoltages (VGS) for the high and low side switches of FIG. 7. As can beseen the gate-source voltages alternate between positive and negativevalues and thus are sufficient to turn the switches OFF when desired. Inaddition, the SWN of the circuit of FIG. 7 is illustrated.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

1. A driving circuit for a half bridge utilizing bidirectionalsemiconductor switches comprises: a high side driver operable to controla high side bidirectional semiconductor switch, wherein the high sidedriver provides a negative bias voltage to the high side bidirectionalsemiconductor switch to turn the high side bidirectional semiconductorswitch OFF; a low side driver operable to control a low sidebidirectional semiconductor switch; an external voltage source whereinthe a negative terminal of the voltage source is connected to the highside driver; and a high side driving switch, positioned between thenegative terminal of the voltage source and the high side driver andoperable to connect the high side driver to the negative terminal of thevoltage source when the low side driver turns the low side bidirectionalsemiconductor switch ON.
 2. The driving circuit of claim 1, wherein thehigh side driver is controlled by a high side input control signal. 3.The driving circuit of claim 1, wherein the low side driver iscontrolled by a low side input control signal.
 4. The driving circuit ofclaim 3, wherein the low side driver further comprises: a firsttransistor; a second transistor, wherein the first transistor and asecond transistor are positioned as a push-pull pair and wherein thefirst and second transistors are turned ON and OFF based on the low sideinput control signal; a power MOSFET placed in series with the low sidebidirectional semiconductor switch; and an output node positionedbetween the first and second transistors and connected to a gate of thepower MOSFET, wherein when the voltage value of the output node turnsthe power MOSFET ON, the low side bidirectional semiconductor switch isON and when the voltage value of the output node turns the power MOSFETOFF, the low side bidirectional semiconductor switch is OFF.
 5. Thedriving circuit of claim 4, wherein the low side driver furthercomprises a desaturation control device coupled to the power MOSFET toensure that the power MOSFET does not operate in saturation.
 6. Thedriving circuit of claim 3, wherein the low side input control signalfurther controls the a high side driving switch, such that the negativeterminal of the voltage source is connected to the high side driver whenthe low side bidirectional semiconductor switch is turned ON and whereinthe negative voltage of the negative terminal is utilized to turn thehigh side bidirectional semiconductor switch OFF.
 7. A driving circuitfor a half bridge utilizing bidirectional semiconductor switchescomprises: a high side driver operable to control a high sidebidirectional semiconductor switch, wherein the high side driverincludes a linear regulator control device that selectively connects thehigh side driver to a lower rail of the half bridge: and a low sidedriver operable to control a low side bidirectional semiconductorswitch.
 8. The driving circuit of claim 7, wherein the linear regulatorcontrol device connects the high side driver to the bottom rail of thehalf bridge when the high side bidirectional switch is ON and when avoltage across a capacitor across the high side driver rises above athreshold voltage, such that the high side driver applies a negativebias voltage to a gate of the high side bidirectional semiconductordevice to turn it OFF.
 9. The driving circuit of claim 8, wherein thelinear regulator control device connects the high side driver to thebottom rail of the half bridge when the voltage across the capacitordrops below the threshold value.
 10. The driving circuit of claim 7,wherein the low side driver further comprises: a first transistor; asecond transistor, wherein the first transistor and a second transistorare positioned as a push-pull pair and wherein the first and secondtransistors are turned ON and OFF based on the low side input controlsignal; a power MOSFET placed in series with the low side bidirectionalsemiconductor switch; and an output node positioned between the firstand second transistors and connected to a gate of the power MOSFET,wherein when the voltage value of the output node turns the power MOSFETON, the low side bidirectional semiconductor switch is ON and when thevoltage value of the output node turns the power MOSFET OFF, the lowside bidirectional semiconductor switch is OFF.
 11. The driving circuitof claim 10, wherein the low side driver further comprises adesaturation control device coupled to the power MOSFET to ensure thatthe power MOSFET does not operate in saturation.
 12. A bidirectionalswitching circuit comprising: a high side bidirectional semiconductorswitch; a low side bidirectional semiconductor switch connected inseries with the high side bidirectional semiconductor switch; and adriving circuit in accordance with claim
 7. 13. A bidirectionalswitching circuit comprising: a high side bidirectional semiconductorswitch; a low side bidirectional semiconductor switch connected inseries with the high side bidirectional semiconductor switch; a highside driver operable to control the high side bidirectionalsemiconductor switch, wherein the high side driver provides a negativebias voltage to the high side bidirectional semiconductor switch to turnthe high side bidirectional semiconductor switch OFF; a low side driveroperable to control the low side bidirectional semiconductor switch; anexternal voltage source wherein the a negative terminal of the voltagesource is connected to the high side driver; and a high side drivingswitch, positioned between the negative terminal of the voltage sourceand the high side driver and operable to connect the high side driver tothe negative terminal of the voltage source when the low side driverturns the low side bidirectional semiconductor switch ON.
 14. Thebidirectional switching circuit of claim 13, wherein the high sidedriver is controlled by a high side input control signal.
 15. Thebidirectional switching circuit of claim 13, wherein the low side driveris controlled by a low side input control signal.
 16. The bidirectionalswitching circuit of claim 15, wherein the low side driver furthercomprises: a first transistor; a second transistor, wherein the firsttransistor and a second transistor are positioned as a push-pull pairand wherein the first and second transistors are turned ON and OFF basedon the low side input control signal; a power MOSFET placed in serieswith the low side bidirectional semiconductor switch; and an output nodepositioned between the first and second transistors and connected to agate of the power MOSFET, wherein when the voltage value of the outputnode turns the power MOSFET ON, the low side bidirectional semiconductorswitch is ON and when the voltage value of the output node turns thepower MOSFET OFF, the low side bidirectional semiconductor switch isOFF.
 17. The bidirectional switching circuit of claim 16, wherein thelow side driver further comprises a desaturation control device coupledto the power MOSFET to ensure that the power MOSFET does not operate insaturation.
 18. The bidirectional switching device of claim 17, whereinthe low side input control signal further controls the high side drivingswitch, such that the negative terminal of the voltage source isconnected to the high side driver when the low side bidirectionalsemiconductor switch is turned ON and wherein the negative voltage ofthe negative terminal is utilized to turn the high side bidirectionalsemiconductor switch OFF.